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<span id="Designators"></span><div class="header">
<p>
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<hr>
<span id="Designators-1"></span><h4 class="subsubsection">1.4.1.12 Designators</h4>
<p>A <i>designator</i>
<span id="index-designator"></span>
is an <i>object</i> that denotes another <i>object</i>.
</p>
<p>Where a <i>parameter</i> of an <i>operator</i> is described as a <i>designator</i>,
the description of the <i>operator</i> is written in a way that assumes that
the value of the <i>parameter</i> is the denoted <i>object</i>;
that is, that the <i>parameter</i> is already of the denoted <i>type</i>.
(The specific nature of the <i>object</i> denoted by
a “<<<i>type</i>>> <i>designator</i>”
or a “<i>designator</i> for a <<<i>type</i>>>”
can be found in the Glossary entry for “<<<i>type</i>>> <i>designator</i>.”)
</p>
<p>For example, “<b>nil</b>” and “the <i>value</i> of <b>*standard-output*</b>” are operationally
indistinguishable as <i>stream designators</i>. Similarly,
the <i>symbol</i> <tt>foo</tt> and the <i>string</i> <tt>"FOO"</tt>
are operationally indistinguishable as <i>string designators</i>.
</p>
<p>Except as otherwise noted, in a situation where the denoted <i>object</i>
might be used multiple times, it is <i>implementation-dependent</i>
whether the <i>object</i> is coerced only once or whether the coercion occurs
each time the <i>object</i> must be used.
</p>
<p>For example, <b>mapcar</b> receives a <i>function designator</i> as an argument,
and its description is written as if this were simply a function. In fact, it
is <i>implementation-dependent</i> whether the <i>function designator</i> is
coerced right away or whether it is carried around internally in the form that
it was given as an <i>argument</i> and re-coerced each time it is needed. In most
cases, <i>conforming programs</i> cannot detect the distinction, but there are some
pathological situations (particularly those involving self-redefining or
mutually-redefining functions) which do conform and which can detect this difference.
The following program is a <i>conforming program</i>, but might or might not have
portably correct results, depending on whether its correctness depends on one or
the other of the results:
</p>
<div class="example">
<pre class="example"> (defun add-some (x)
(defun add-some (x) (+ x 2))
(+ x 1)) ⇒ ADD-SOME
(mapcar 'add-some '(1 2 3 4))
⇒ (2 3 4 5)
<i>OR</i>⇒ (2 4 5 6)
</pre></div>
<p>In a few rare situations, there may be a need in a dictionary entry
to refer to the <i>object</i> that was the original <i>designator</i>
for a <i>parameter</i>.
Since naming the <i>parameter</i> would refer to the denoted <i>object</i>,
the phrase “the <<<i>parameter-name</i>>> <i>designator</i>”
can be used to refer to the <i>designator</i> which was the <i>argument</i>
from which the <i>value</i> of <<<i>parameter-name</i>>> was computed.
</p>
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